1. Field of the Invention
The present invention pertains to a method for the preparation of a liquid concentrate from which a metal cleaning solution may be prepared by dilution with additional water. More particularly, the present invention pertains to the method of preparing a liquid concentrate from which a dilute metal cleaning solution may be obtained which is suitable for the removal of smut, oxide films, conversion coatings, tarnish and scale from aluminum, brass and copper. Even more particularly, the present invention concerns the preparation of non-chromated baths and additives therefor useful for cleaning metal surfaces.
2. Prior Art
The post-cleaning of metal surfaces after caustic etching or oxidation has most often involved treating the metal surface with an acidic solution of nitric acid, sulfuric acid, hydrofluoric acid, mixtures thereof and the like.
To remove oxide films, conversion coatings and the like from metal surfaces, mixed acid pickling baths containing chromic acid are most conventionally employed.
For a general discussion of acid cleaning baths, see Murphy, J. A., Surface Preparation and Finishes for Metals, 1st Ed., McGraw-Hill Book Company, New York, N.Y., (1971) at pp. 46-57.
Chromic acid baths inherently create waste disposal problems thereby somewhat negating their utility. The other acid baths have rather limited application since they can only remove smut from caustic etching and the like.
Accordingly, in the prior art, cleaning compositions employing ferric sulfate have been developed to overcome these problems. These compositions, however, were prepared only as a dry concentrate or as the ultimate dilute cleaning solution.
Subsequent to the development of such compositions it became desirable to prepare a liquid concentrate containing from 10 to 60 percent by weight of water for marketing purposes. However, attempts to prepare such concentrates by simply dissolving the dry ferric sulfate compositions in water failed since these compositions would not dissolve completely in such small amounts of water.